In recent times, the use of lightweight battery materials and cost efficient battery constructions have been or prime interest to the automotive and battery industries. In particular, the use of shunt-current protected systems are of recent interest. U.S. Pat. No. 4,346,150; issued: Aug. 24, 1982, teaches a low-cost, lightweight, shunt-current protected battery system featuring a stack of cells constructed of alternating plastic sheets comprising separators and electrodes.
The present invention is an improved construction over the manifold-protected design illustrated in the aforementioned patent. The current invention seeks to provide a tunnel protected electrochemical device which optimizes the auxiliary power requirements for operating the cell; i.e. a cell which uses the least amount of energy to both hydraulically pump the electrolyte through the cell, and to electrically protect against shunt currents.
In manifold shunt current protected cells, the hydraulic pumping power tends to decrease with increasing manifold diameters. However, the power required to protect against shunt currents increases as the second power of the manifold diameter. Thus, the protective power to the manifold and the pumping power are inversely coupled.
With the tunnel protection power system, the protective power is less than the manifold protective power. As the diameter of the manifold increases (for a fixed geometry of connections between the manifold and the cells) the protective power through the tunnel asymptotically approaches a maximum. The tunnel protective power becomes essentially independent of the manifold diameter at larger diameters of the manifold. Thus, the summation of the pumping and tunnel protective power has a lower power requirement than the manifold case and has a minimum value at a lower value than the manifold system.
The present invention seeks to optimize the design of a tunnel protected electrochemical device, such that manifolds, tunnels and channels provide for the least consumption of auxiliary power during operation of the system. The invention also seeks to decouple the protective power requirements from the hydraulic pumping power requirements.
The subject invention is useful in the manufacture, construction and assembly of many different kinds of electrochemical cells, and the invention should be interpreted as not being limited to a specific system.
It is of particular interest for use in a circulating zinc-bromine battery, constructed in accordance with the teachings advancing in the aforementioned U.S. Pat. to: Agustin F. Venero, entitled: Metal Halogen Batteries and Method of Operating Same, U.S. Pat. No. 4,105,829, issued: Aug. 8, 1978, and assigned to the present assignee.
The above-mentioned battery system is of particular interest because of its low cost and availability of reactants, its high cell voltage and its high degree of reversibility.